System of electric-motor control.



G. BAEHR.

S SYSTEM OF ELECTRIC MOTOR CONTROL.

WITNESSES ATTOf iNEY UNITED S ATES- PATENT OFFIGE.

"GEORGE IBAEHR, or uon'r'cnnrn, NEW, JERSEY, assmnon 'ro wEs'rmGnoUsEELEc- TRIO AND MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA.

SYSTEM OF ELEcrmc-Mo'ron oon'rnon.

Specification of Letters Patent.

Patented Mar. 25,1913.

Application filed December 29,1909. Serial no. 535,400.

To all whom. itmay concern:

Be it known that I, GEORGE BAEHR, a cit1-' vzen of the United States, and a resident of -following is a T tioularly adapted for skip-hoist or elevator motors.

the motor to rest at predetermined points in its operation in either direction and means dependentupon the motor 'l0&d for. So governing the application of the brakes as to secure equal and uniform retardation, irrespective of the motor load.

In blast furnace skip hoist control systems, there are usually three different loads to be taken a into consideration-,as follows: first, when the skip cars are filled with ore; sec-' ond, when the ski cars are filled withcoke'; third, when the s i cars are empty. .It is particularly desira le for this service to maintain a uniform speed for the cars at a predetermined distance from the limit of travel or stopping point, irrespective of the loads which they are carrying. In order to secure this result, the retardation of the operating motor must be substantially uniform, irres ective of the motor load. In other wor s the motor must always be brought to rest in equal retardation periods.

According to my present invention, I rovide a system of electric motor control w ich may be utilized for various purposes but.

which is specially designed to meet the requirements for automatically operating skip hoists for'blast furnaces. In retardin the electricmotorat predetermined limits n; its operationyl emplo ia re-generative'braking arrangement and automatically yaryi'the amount of resistance iiioluded in the regenerativecircuit according to the motor speed, which [varies to a'certain extent with the motor load.

The single.- figure' off the accompanying drawing is a diagrammatic view showing. thecircuit connectionsl'of a system oi-con-z I by -the position oi the contact arm 52 of the trol embodying my invention.

' Referring to the drawing, the system here shown comprises an electric motor 1, havmg an armature 2, a series. field ma et winding 3 and a shunt field magnet wmding 4; 'a resistance comprising aplurality of sect1ons5 to 11 inclusive, a master switch 12, a limit switch 13, manually operated breaker 32, brake magnets 33 and 34 and a plurality of relay switches 41, 42, 43, 44, 45, 46 and47. 1

Direct current energy is supplied from any suitable source through circuit conductors 48 and 49.,to-brushes 50 of the motor 1 and the control circuits of the system are supplied with energy from the same source, with the exception of the relay switches 41, 42 and 43 which are supplied with energy from alternating current collector rings 35, 36 and 37 with which the armature 2 of the motor 1 is provided. The collector rings are connected to suitable points in'the armature winding and are engaged by stationary contact brushes 38, 39 and 40. Themagnet windings oftherelay switches 41, 42 and 43 are so designed that the alternating current voltage, generated in the mo-- tor armature, under maximum load, will not actuate any of-them but, under medium load on the motor 1 the relay 41 will be actuated,- and under minimum loadconditions. relay switches 41 and 42 will both be actuated.

Under normal operating conditions, relay.

10% above normal) it will-be actuated and I will interrupt the motor circuits as herein after pointed out. and 42 serve to short-circuit sections of the regenerative brake resistanceso that the regenerative braking action shall be a maximum when the load is'a" minimum, and vice i The operation of and the circuit connections for the system are as follows: Assuming that the switches occupy the positions shown in the drawing and that the motor has been brought to rest by the limit switch 13- at one extremity of its travel, as indicated The relay switches 41' limit switch 13; if the master controller 12 is moved to occupy the position 3 circuit connections are established as follows: A shunt field circuit is established from the positive line conductor 48, through conductor 53, switch 18, conductor 54, magnet coil 47, conductor 55, shunt field m'agnet winding 4, condu'ctor56, switch 18 and conductor 57 ductor 70 which through 'theswitch 14 to the negative line to the negative line conductor 49. The completion of this circuit closes the relay switch 47. A circuit is completed through the magnet winding of relay 45, from conductor 48, through main line switch 14, series coil 58 of the circuit breaker 32, conductor 59, winding 45, conductor 60, contact fingers 61 (which are bridged by the contact member 62), conductor 63, contact members 64 and 65 (which are bridged by the arm 52), conductor 66, contact fingers, 67 (which are bridged by the contact member 68), conductor 69 and switch 17 to the negative conis connected directly conductor 49. A circuit for the relay mag- -net winding 44 is completed from conductor ductor 59, through conductor 76, circuit breaker 32, conductor 77, switch 17, conductor 78, relay switches 45, 43 and 47, conductor 79, magnet coils of switches 22 and 23, conductor 80, fingers 81 (which are bridged by the contact member 82, except when the limit switch 13 occupies its oppo site extreme position), conductor 83 and conductor 69 to the negative conductor 70.

As soon as reversing switches 22 and 23 are closed, a motor circuit is established from relation with the armature, the motor will switch 22, conductor 100, series field ma conductor 59, through reversing switch 23,

, conductor 96, commutator 51 of the motor 1,

conductor 97, magnet winding of relay switch 28, conductor 98, resistance sections 8, 7, 6 and 5, conductor 99, motor reversing et winding 3, brake magnets 33 and 34, con uctor 101 and switch 14 to the negative conductor 49. The motor circuithaving been completed with suitable'resistance in series be started andthe series relay switch 28.will

be temporarily energized.

, When the motor reverse switches 22 and c .23 are"closed,- the rela'ys'witches 84 and 85 with which they areprovided are also'closed and a control circuit is then completed from conductor 77, through said relay switches,

conductor 86, magnet winding of relay 46, conductor 87, switch 15, conductor 88, contact fingers 89 (which are bridged by the contact member 90), conductor 91 to contact 24, conductor 95 and relay switch 46 to the.

ne ative conductor 70. The accelerating switch 24 is thus energized as soon as the series relay is closed, and short-circuits the resistance section 5. When the accelerating switch 24 closes, a relay switch 102, with i which it is provided, is also closed and a control circuit is then completed'through its magnet winding independently of the-relay switch 28, in a well known manner, another control circuit through the relayswitch being completed-through the magnet winding of the accelerating switch 25. This action is repeated and the accelerating switches are successively actuated to short-circuit the resistance sections 5, 6, 7 and 8, the accelerat: ing action being delayed by the series relay in order to prevent injury to the motor armature. v

The limit switch 13 is mechanically'connected to the shaft 2 of the motor 1, either directly or indirectly, by gearing or otherwise so that the arm '52 rotates in a counterclockwisedirection and successively engages the contact ring segments 103, 104 and 105. As soon as the arm 52 moves out of its extreme position, the switch 82, which corresponds to the switch 82, is permitted to close, and, when the arm engages the segment 103, the control circuit through the magnet winding of the relay 45 is completed from conductor 60 directly to con-- ductor 66 through the arm 52, making this circuit independent of the master switch 12. When the arm engages the contact ring segments 104 and 105, relay switches 44 and 46 are also independent of-the master switch. It is evident, therefore, that it is only necessary to move the master switch to the position 3/ for a very short time after which it may be returned to its ofi tion of the system being automatic thereafter. The mechanical structure of the master switch is preferably such that as soon'as its position, the opera-.

operating lever is released by the attendant,

it will automatically return to its ofi position.

It will be readily understood by those skllled in the art that the speed ratio between the shaft of the. motor 1 and the contact arm 52 of the limit switch may be such that the operation of the motor may continue to any predetermined point' in its 25 contact brush 38, through conductor 107to travel beforeitis automatically brought to rest. When the contact arm approaches the 'opposite extremity of its travel from that which is indicated in the drawing, it first moves out of engagement with the contact ring segment 105 and into engagement'with the segment 106.- In becoming disengaged from the segment 105, the circuit which was completed from'the relay 46 is interrupted (themaster switch being in its oil position). It follows that the relay switch opens and the accelerating switches 24, 25, 26 and 27 are also opened and the motor armature resistance is reinserted. This is the first step in retarding the speed of the motor. The contact arm '52 is next disengaged' from the ring segment 104, thereby interrupting the circuit of the relay 44 an permitting this switch to close.

When the relay switch 44 is closed, the

' magnet windings of the relay switches 41 and 42 are energized from the alternating circuits which are supplied with ener from the brushes 38, 39 and 40. The c1rcuits may be traced as follows: from the one terminal of the-magnet winding of the relay switch 42, through the inductive resistance 108 and directly to one terminal of the magnet winding of the switch 43. The opposite terminal of the switch 43 is connected through the inductive resistance 109 and conductor 110 to contact brush 39.

The contact brush 39 is also connected 85 through'one section of the relay switch 44 andthrough inductive resistance 111' to one termlnal of the relay switchmagnet 41, the

opposite terminal of this magnet being connected through conductor 112 to contact brush 40. The brush 39 is also connected to the opposite terminal of the magnet 42 through a section of the switch-44. If it is assumed that the ring segments 35, 36 and 37 are connected to three equally spaced points in the motor armature winding, the voltage between any two of the conductors 107, 11.0 and 112 will be equal, as in any three-phase alternating current circuit, and it is evident from the circuit connections above traced that the magnet windings of the relays 41, 42 and 43 are energized by being connected to different legs of this three-phase circuit. The Voltage applied toconditions; only the switch 41 under me dium load conditions, and none of them will be actuated under full load conditions.

If it isfirst assumed that the motor speed is excessive so that the relay switch 43 is actuated, it is evident, from the circuit-[com nections already traced, that the motor reversing switches will be opened and, since this relay switch is independent of the switch 44, the motor circuit ma be interrupted at any time, if its spec is abnormally high. If it is assumed that the motor is operated under minimum load, both the relay switches 41 and 42 will be closed and circuits will be established as follows: from conductor 77, through relay switches 84 and 85 to the magnet windings of the switches 30 and 31. From magnet winding 30, circuit is completed through a conductor 113 and relay switch 41 to negative conductor 70. From the winding of the switch 31, a circuit is similarly completed through the relay 42. Therefore, under the conditions above assumed, both the switches 30 and 31 will be closed. When the relay switch 44 was first deenergized and close by reason of the. disengagement of the arm 52- from the segment .104, a circuit was completed from conductor 59, through 'co'ndu'ctor 114, magnetwinding of'switch 29,

conductor 115 and one section of relay switch 44 to negative conductor 70 through switch 17, the switch 29 being consequently closed. A circuit is established, as soon as the switch 29 is closed, from the commutator brush 50 of the motor 1, through conductor '96, switch 29, conductor 116, resistance sections 11, 10 and 9, conductors 98 and 97 to the opposite commutator brush, The motor will operate as a generator by reason of its momentum and will, therefore, su ply energy to the resistance sections 9, 10 an .11. The braking effect. of this connection upon the motor iswell known and its intensity is dependent upon the'amount of resistanceincluded in the amature circuit. If both the switches 30" and 31 are closed in addition to the switch 29, as in one of the cases assumed when there is a minimumjload, only the resistance section-9 will be connected in 1 the local circuit so that the intensity of the braking effect will be increased. If only the switches '29 and 30 are closed, the arrangement of the resistanceis such that the braking effect will be less in intensity than whenboth are closed, but greater in intensity than when neither of them is closed; The contact arm 52 and the ring segment 103 are so arranged that the. former will be se arated from the latter'at the same time t at the I with an .electric motor, a supply circuit motor to rest, and means dependent upon the a therefor, and limiting means for automatically mterrupting the supply circuit at a predetermined point in its travel, of retarding means dependent upon the speed. of the motor at the time the motor circuit is interrupted for bringing the motor to rest in substantially equal retardation periods.

2. In a control system, the combination with an electric motor. means for accelerating the motor and limiting means for bringing the motor to rest at a predetermined point in its operation, of means for utilizing the momentum of the motor at the time its circuit is interrupted for bringing the motor speed at the time the supply circuit is interrupted, for varyingt-he degree of braking.

3. In a control system, thecombination With an electric motor, means for accelerating the motor and limiting means .for bringing the motor to rest at a predetermined point in its operation, of means for shortcircuiting the motor armature through an external resistance upon theinterruption of the motor circuit and means dependent upon the motor speed at the time its supply circult is interrupted for determining the value of the resistance included in said shunt circu1-.

4. In a control system, the combination with an electric motor, means for accelerat mg the motor and limiting means for interrupting the motor circuit ata predetermined point in its operation, of means dependent upon the interruption of the motor circuit for short-circuiting the armature through an-external resistance, and means dependent upon the alternating current voltages generated in the armature winding at the time the circuit is interrupted for varying the amount of said external resistance.

5. In a system of control, the combination with a direct current electric motor having alternating current collector rings and external circuit connections and direct current supply circuits, and switches for short-cirtor armature through an external resistance,

and a lurality o-f. relay switches dependent upon the electro-motive forces generated in the motor armature winding for varying the amount of said. external resistance, whereby the retardations of the motor may beuni; form and independent of the motor load.

7. In a control system, the combination with a direct current electric motor having external means for utilizing the alternating current electro-motive forces generated in the motor armature and means for inter rupting the motor supply circuit and for short circuit-ing the motor armature through an external resistance, of means governed by the alternating current electro-motive forces ling the amount of external resistance in ,cluded in the aforesaid short circuit.

In testimony whereof, I have hereunto subscribed my name this 18th day of December. 1909. v

. GEORGE BAEHR. Witnesses:

. JoHN' Fox. DAVID J. MAHONE.

generated in the motor armature for control- 

